DE1614607A1 - Ring laser device - Google Patents

Description

Υ Al fcM IANWALIt

DIPL.-ING. CURT WALLACH

DiPL.-ING. GÜNTHER KOCH JO 1

DR, TINO HAIBACH

-SO, September 1967 11 033 - Wg / Re

Sperry Rand Corporation, Hew York, V »St.A,

Ring laser device

The invention "relates to ring lasers and" particularly on gate directions to reduce the coupling between opposing coherent light rays progressing in the ring laser c .-. \ _

Bin Hing Laser. "/ Eist a \ mi arranged laser source Va 'in a planar optical hollow., Wherein the optical cavity by three or more highly reflective corner members is formed, the radiation emitted by the source. · Guide light rays progressing in the opposite direction around a closed loop path. Can any laser-active medium be used as the laser source? however, a laser gas mixture enclosed by a hollow tube was preferred because, in the current state of the art, such lasers easily resemble an undamped type

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■ shaft can be operated. In general, Brewsterwinkel windows to seal the ends of the hollow tube and to Used to determine the polarization of the light waves emitted by the source, although other common sealing and polarizers were used. The optical cavity vibrates at those frequencies for which the optical length of the closed loop of a whole Number of light beam wavelengths corresponds. Therefore, if ™ their optical path lengths are identical, they will vibrate opposing light rays at the same frequency! for unequal path lengths, they oscillate at different frequencies that are determined by one of the difference their path lengths are separated by a proportional size. One Possibility to produce tintersheiiieher '/' egg lengths

around a bestent in the rotation Jes ßii: *;:. utiers ^ / r-ur level of the closed loop paths vertical axis »In üieaeir. Example is the one propagating in the direction of rotation Light beam traversed a greater distance in order to turn to its starting point in the closed To arrive at the loop path while the oppositely directed "beam traverses a correspondingly shorter distance. As a result, it swings in the direction of ring rotation propagating light beam at a lower frequency than it would in the absence of rotation did because a longer wavelength meets the vibration requirement. In a similar way, the one swings against the

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Direction of rotation of the light beam "at a higher frequency ^{.; X}

The speed of rotation or the difference in travel length is
usually measured by extracting (decoupling) a small portion of the energy in each light beam from the ring by 'partial transmission' by one of the members Photodetector in which it is used to generate a difference between the frequencies of light rays
proportional beat frequency signals are superimposed. For a relatively fast rotation, the Schwelrungsfrequena depends linearly on csr ¹ rotation speed at, ar er at ^; Decrease in speed -.vira this dependency:? O: li.eiilich nichulinear because of the coupling,
scattered component of the oppositely progressing ί ray. The backscatter i? R to a certain extent zn
always present, but it only creates a coupling. cei
■ relatively low brewing rates, moreover
The coupling normally becomes more pronounced when the optical length decreases * "" If the rotational speed is reduced even further, the coupling finally becomes strong enough to prevent the sudden cessation of the beatings.
to effect frequency, and indeed because the contrary— ■

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directional beams synchronized at the same frequency will. This frequency synchronization phenomenon ^ is referred to as mode locking, and the corresponding beat frequency or rotational speed, at which this phenomenon occurs is called the mode locking threshold

The backscattering is caused by dust particles, interfaces between media with different refractive indices and imperfections in the components contained in the ring. Careful control of the environment to remove the dust and the use of high quality optical components with precision optical surfaces significantly reduces backscatter and lowers the mode lock threshold. But, even with these refinements, the Möde locking threshold is suitable for many applications. . , still too high. Therefore, known ring laser often contained ■ to bypass the mode-locking problem, devices such as a light-propagation device which different propagation constants for light beams with any 'having different characteristic difference. An example of such a device is an electro-optic birefringent material with orthogonal major axes in which plane polarized light waves which are aligned parallel to the "corresponding major axes" travel at different speeds.

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¹ As a result, a nominal difference path length and corresponding floating or biasing frequency are generated for the light beams, even when the hanging is in the stationary state * The rotation then increases or decreases the beat frequency depending on the direction of rotation from its nominal value. The dynamic operating range of the ring laser as a rotary sensing instrument is thus determined by the difference between the nominal bias frequency and the mode locking threshold, unfortunately the birefringent material and the components still present to produce the orthogonality between the orientation of the oppositely polarized beams generate additional Backscatter, whereby the mode locking threshold is even higher and the dynamic operating range is reduced proportionally.

It was observed that for the occurrence of the coupling, the backscattered component of the one ray of light and the oppositely progressing ray of light is identical must be polarized. It was also found that the highly coherent rays of light emitted by a laser are only slightly depolarized in the case of backscattering by a reflection part, with the result that the reflected components of plane polarized and circular polarized light retain their original polarization, with the exception that the Sijan-'des is circular

polarized light is reversed, i.e. when the incident If light is polarized in a right 8-circular manner, it becomes left-polarized after reflection and vice versa. Consequently the coupling tendency is increased when the oppositely directed light beams at a common Funct of the optical cavity have the same polarization. This was actually the case with the known ring lasers

) is the case because the Brewsterwinkel windows at the ends of the With the laser tube, only plane polarized light with a prescribed orientation passes through the laser medium let »Nonetheless, this mode of operation was preferred because it not only ensures that the optical Path lengths of the opposing light rays neither through stresses in the Brewster angle windows nor through random time-varying birefringence of the laser medium be influenced and also compatible with the requirement

. is that just polarized light rays are either parallel or must be polarized perpendicular to the plane of the ring in order to be in the light rays reflected from the corner members ■ Avoid distortion, i.e. elliptical polarization.

In current practice it was usually perpendicular

i Polarization is preferred because it keeps the losses caused by absorption and permeability of the corner members small.

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! Neither circularly polarized nor vertically or horizontally generate plane polarized light beams.

A main object of the invention is therefore to to create a ring laser, in which the oppositely progressing light beams with respect to each other in such a way are polarized so that the coupling between them is significantly reduced »"

Another object of the invention is to design a ring laser in such a way that the oppositely advancing light beams are polarized with respect to one another in such a way that the mode locking threshold is reduced.

Furthermore, a ring laser is provided according to the invention, in which the oppositely progressing rays of light g are polarized identically only during their passage through the laser medium in order to prevent their optical path lengths in the form of a closed loop are influenced differently, either by temporal changes in the birefringence of the laser medium or by stress effects in the on each Polarizing parts arranged at the end of the laser medium.

Finally, according to the invention, a ring laser is provided,

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at which the amplitude of the transmitted into the laser medium backscattered light is significantly reduced.

; The invention also provides a ring laser in which through the use of a combining device which turns one of the extracted light beams in the opposite direction Direction to its original port propagation direction back into the ring, coupling was essential P is decreased.

Finally, according to the invention, a ring laser is provided in which the oppositely progressing light beams are polarized such that each light beam and a backscattered component of the oppositely progressing Light beam are polarized orthogonally.

. The main task mentioned and its sub-tasks, as well as. further objects of the invention are according to the invention solved by the provision of polarization converters in the path of the oppositely advancing light rays are arranged next to the ends of the laser medium. Each polarization converter represents the polarization of the from near Located end of the laser medium incoming light beam such that at every common point in the optical cavity - except where the laser medium is arranged, each opposing light beam and one backscattered

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Component of the light beam advancing in the opposite direction are orthogonally polarized. The polarization converter also adjust the polarization of the light beams re-entering the laser medium in such a way that the oppositely directed Light beams are identically plane polarized during their passage through the laser medium. In one embodiment According to the invention, the polarization converters are circularly polarizing elements which are plane polarized Convert light rays into circularly polarized light rays that circulate on the circular paths, with the exception of the part between the circular polarizers where the laser medium is arranged. In another embodiment of the invention, the are polarization converters

the

optical rotators, the tfcatxdani plane of polarization

turn

of the light falling on them nm3cäat £ 8X imd thereby plane polarized light. an orientation in plane polarized Convert light of a different orientation. "."

Further advantages and details of the invention emerge from the description of exemplary embodiments on the basis of FIG Drawing »'in the drawing, in the same component with the same reference numerals are provided, shows:

Figure 1 is a perspective view of an embodiment of the invention, in which the opposite

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put rays of light along the main part of the

pins

Suuixif iform paths are circularly polarized;

Figure 2 is a plan view of another embodiment

of the invention, in which the circularly polarized light ring radiate around the main part of the shaped 7 / ege advance around and use a different combining device;

FIG. 3 shows a perspective view of a further exemplary embodiment designed according to the invention, in which the opposing rays of light around the main part of the locee-shaped paths are orthogonally polarized.

In Fig. 1 is a planar triangular optical resonance- cavity shown by three rearview mirrors 10, 11 and 12 formed Bt. Between two adjacent corners is a Tube 14 arranged, which .ein Iaseractive3 medium, such as for example contains the standard helium gas mixture. The gas mixture is generated by a high-frequency generator 15 stimulated in a frequency range from 20 LiHz to 30 LiHz is working; the output signal of the high frequency generator is through lines 16 and 17 to the near the ends of the

t tube arranged ring electrodes 18 and 19 connected.

14th

Optical planes 20 and 21 which seal the ends of the tube / are inclined with respect to the longitudinal axis of the tube by the Brewster angle and act as polarizers, the

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Transmit plane polarized light parallel to the plane of the optical cavity! such light is hereinafter referred to as horizontally polarized. The light rays imitated by each end of the tube 14 are successively reflected by each corner mirror and thus propagate in opposite directions around a common annular (circular) path, vibrating at the same frequency when their optical path lengths are the same. Since the horizontally polarized light lies in the plane of incidence, the oscillating light rays retain their polarization when they are reflected by the corner mirrors. The same process is obtained with plane polarized light with a polarization orientation orthogonal to the horizontally polarized light? Such orthogonally oriented plane polarized light is referred to below as vertically polarized. For any other orientation, the plane polarized light is elliptically polarized when it is reflected by the corner mirror, with the result that the vertically polarized component is strongly attenuated when the light beam re-enters the laser medium. For this reason, the plane polarized, oppositely directed light beams are usually polarized vertically or horizontally and preferably identically, especially when they pass through the laser medium, utr. aas to prevent the occurrence of different path lengths, either through random, time-varying birefringence in the gas mixture or through

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Stress in the optical surfaces with Brewster's angle arise, what can occur if these are not oriented identically. When the path lengths of the closed loop for example, made unequal by rotation about an axis perpendicular to the plane of the laser cavity, oscillate the opposing light rays at different frequencies. However, it is often also desirable that under- ™ There are different path lengths in the closed sole even in the absence of rotation. That goes one not only allows the coupling problem mentioned above, but also allows the determination of the meaning of any other different! speed path length disturbance.

A special device for generating a different (differential) ring-shaped path length has a magneto-optical birefringence member 22, which works in conjunction with the polarization converters 23 and 24. The polarization converters are circular polarizers, i.e. optical waveguide plates made from an inherently birefringent material, such as crystalline quartz with orthogonal, perpendicular to the direction of propagation of the opposing light rays oriented main axes F and S are constructed. Plan as well as light rays poralized parallel to the F-axis propagate through the circular polarizers with greater speed than those parallel to the S-axis

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polarized light rays. The circular polarizers have a thickness parallel to the direction of light propagation such that orthogonally plane polarization Light rays entering the circular polarizers in time phase and aligned with the main axes are, "are 90 ° out of time phase when exiting, so that the exiting light is circularly polarized» TJm both Light beam components parallel to the F and S axes the circular polarizers are available with

Main ο

their / axes oriented at an angle of 45 "with respect to the horizontally polarized light beams. The horizontally polarized CW (= clockwise) light beam 29 transmitted through the optical surface 21 emerges from the circular polarizer 23 as right-hand circularly polarized light and is Represented by the vector 30 "a clockwise - when looking against the direction of light propagation" - rotating light vector is referred to as right-circularly polarized, while a light vector rotating counterclockwise in the same direction of view is referred to as left-circularly polarized

will" -

If the circular polarizers are viewed from a point within the tube 14, the main axes can be seen of the circular polarizer 24 in space quadrature (shifted by 90 °) with the main axes of the circular polarizer 23.

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If, as a result, the circularly polarized CW light beam runs through the circular polarizer 24, it is in horizontally polarized light represented by the vector 31 converted. Similarly, that represented by dashed vector 32 becomes horizontally polarized CCW (counterclockwise) light beam through the circular polarizer 24 in left-circularly polarized, light represented by the vector 33 and then through the circular polarizer 23 in horizontal polaj ized, represented by the dashed vector 34 converted light. Because the sense of rotation is circularly polarized Light rays are inverted each time they are reflected, becomes that represented by vector 30 right-handed CW light beam after incidence on the Mirror 12 left-handed. Similarly, the left-handed CCW light beam represented by the dashed vector 33 becomes clockwise after reflection by mirror 11 and left-handed after reflection by mirror 10. That magneto-optical birefringence part 22 is made of glass or another material thawed, soft the classic one Has Faraday effect. One by a (not shown) permanent or electromagnet to the double mesh part Magnetic PeId H "applied parallel to the direction of light propagation causes the birefringence part different refractive indices for the circularly polarized waves has, for the opposite direction of rotation.

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regarding the direction of the magnetic field. Even though Both the C \ Y and the COW light rays are polarized to the left when passing through the birefringence part their polarization vectors rotate in opposite directions with respect to the direction of the magnetic field. This causes the optical path lengths of the closed loop for oppositely advancing light rays are different, which has the consequence that they vibrate at different frequencies. The ring laser can also be used without a double refraction part 22, but regardless of whether the birefringence part is provided in the optical cavity it should be noted that at every common point in the optical cavity the polarization of the opposite Light rays of the type is that a backscattered component of a light ray opposite the oppositely advancing light beam is predominantly orthogonally polarized, so that they do not cause any coupling since the backscattered components do not transmit f through the optical surfaces into the laser medium will. The corner mirrors are preferably constructed from multilayer dielectric in order to be circularly polarized Light rays to minimize distortion and energy loss.

To achieve a rigid structure with reduced energy loss obtained, can the optical cavity be constructed as shown in Figure 2? Figure 2 is the same as Figure 1 with the exception

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agree that the circular polarizers 23 and 24 are different arranged and prisms 36 and 37 are also provided. The energy loss is reduced because of the refractive index of the Prisms corresponds to the refractive index of the optical surfaces and circular polarizers. In addition, the geometry of the cavity be set so that the opposing light rays on the backs 38 and 39 of the Prisms 36 and 37 strike at an angle which is greater is than the critical angle so as to produce total internal reflection. In this embodiment, the difference between the frequency of the opposing light rays measured in such a way that one part of the Energy in each light beam transmits through corner mirror 10 to a combining device which transmits the transmitted Rays collinear and spatially coincident for use in a photodetector in which they are used Making a beat frequency signal proportional to the difference between the frequencies of the light beams are superimposed. The part of the CW light beam transmitted through the corner mirror 10 runs directly to the analyzer and on the photodetector 26. The portion of the CCW light beam extracted from the laser cavity is perpendicular Incidence on a mirror 28 and is reflected back on the corner mirror 10. The corner mirror 10 is the largest Part of the energy in the extracted GCT light beam to the analyzer 25 reflected on the photodetector 26, namely

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in colinear relation to the extracted CW light beam, but with some of the energy back into the Baaerhohlraum is transferred where it is contrary to its original direction continues. Since the transferred back into the cavity Part of the extracted OOW beam polarized orthogonally is with respect to the CW-ray advancing in it, these rays do not couple. As a result, the propagation of the appropriately oriented circularly diminishes polarized light rays around a main part of the All around, not only the coupling caused by internal backscattering, but also that by using a coupling generated by a simple combining device. The analyzer 25 is provided to identify identically polarized components of the extracted light rays, since the photodetector did not polarize orthogonally circular Radiance appeals.

In dei in lig, 1 illustrated embodiment of the ■ Invention, a slightly different combining device is used. The CCW light beam emerges from the optical cavity Taken by partial transmission by means of the mirror 10 so that it hits the beam splitter 40 and the Photodetector 26 is reflected. The -'CW-ray becomes | but removed by partial transmission by means of the mirror 12 and then from the mirror 41 to the beam splitter 40 reflected so that the

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carried component colinear with the extracted CCW light beam for application on photodetector 26 is where these rays produce a difference between the frequencies of the opposing light rays proportional

f frequency
bunga signals are superimposed. Since the direction of rotation of the circularly polarized light beams "reverses" on reflection, but remains unchanged when transmitted through an object, the two collinear light beams are polarized to the left and therefore no extraction analyzer is required for superimposition.

The arrangement according to -Pig. 3 corresponds to that of FIG. 1 with the exception that here the Brewster angles of the optical surfaces have different orientations and different elements are used for polarization converter and birefringence part magneto-optical see birefringence part of 2% according to Fig. 1 the same, except that they are specially adapted to a 45 ° rotation to produce a 'running through them plane polarized light beam. the birefringence member 47 can be either natural or electrically induced birefringence refer-

i borrowed the main orthogonal axes, namely wis in the quarter-wave plates operating as circular polarizers in FIG. 1. The tube 14 is arranged so that the transmitted through the optical surfaces 20 and 21

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CCW and CW light beams are oriented like this is represented by the dashed vector 4δ and vector 49, respectively. The CCW light beam 46 becomes through the Faraday rotator

43 rotated by 45 ° and is thus - as indicated by the dashed Vector 50 indicated - vertically polarized. In a similar way The CW idling vector 49 is made by the Faraday rotator

44 rotated by 45 ° and is - as indicated by the vector 51 - horizontally polarized. The birefringence part 47 is oriented with its main axes parallel with respect to the horizontally and vertically polarized light rays, whereby a different path length is generated for the oppositely directed light rays, even when the optical cavity is stationary. When the CCW light beam passes through the rotator 44, its plane of polarization is rotated 45 ° into the position of the dashed vector 52, whereby it can pass through the optical surface. Similarly, the CCW light beam is turned into the | indicated by the vector 53 by the rotator 43 Position rotated by 45 ° so that it can run through the optical surface 20.

It should be noted that at all points along the annular path - with the exception of the area between the rotors where the laser medium is arranged - the light beams are orthogonally plane polarized. Therefore, as explained above, there is no coupling between a backscattered oirponeirte

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of a ray with the opposite advancing Beam on. The combination shown in Figures 1 and 2

got
Devices, as well as other / combining devices, can be used to measure the difference between the frequencies of the opposing light beams. Since the orthogonal plane polarization of the light beams avoids the above-mentioned external retroreflective problem described with reference to FIG. 2, the simple combining device of this embodiment is generally preferred because it is easier to set up and align. In this example, the transmission axis of the analyzer 25 must be oriented at an angle of 45 ° with respect to the plane of polarization of the light beams taken out, because the light beams are plane polarized.

Refractive elements can also be used instead of the reflection parts in order to divert the light rays along ring-shaped (circular) Because of to conduct} furthermore, some or all of the optical path lengths can be curved or non-planar be. In addition, the gaseous laser medium can be excited by a halogen voltage source and other known laser media can be used.

Claims ·.

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ORIGINAL, fNSPECTED

Claims (1)

16148Ö7 Claims | 1. Optical device with two light beams advancing on ring-shaped paths in opposite directions as well as with devices · for the construction and operation of this device! in order to minimize the adverse effects created by rtlokge it scatters light within the annular paths, characterized by the following combination t . (a) Devices for forming an optical cavity in the form of a closed loop! (b) a laser source (H) for generating oppositely directed? Light rays that run in opposite directions around the ring-shaped paths determined by the optical cavity:? J- \ ^: (c) near each end of the laser source (14) in the annular | Because of such arranged polarization converters C43r 44) that Asm between the polarization converters via the laser source -Ί- measured is a smaller part of the annular path lengths and wherein each of the polarization converters is adjusting the polarization of the on it from the adjacent end of the Laser source incident light beam so that at a common point of the ring-shaped paths - with the exception of the mentioned smaller part - the closely opposing ones Rays of light and the predominant part of a backward 009828 / '147 4' originally inspected 16U607 scattered component of the oppositely progressing light beam are orthogonally polarized, and wherein the polarization of the oppositely directed set light beams is reset so that they are plane polarized identically to the mentioned smaller part, (d) devices for extracting part of the energy from the optical cavity from the opposing ones Light rays to generate first and second extracted light rays. $. Device according to claim 1, characterized in that that in the ring-shaped paths devices are arranged which a difference in the ring-shaped (circular) Generate path lengths of the opposing light rays. 3. Device according to claim 1, characterized in that the polarization converter (43 _f 44) are quarter-wave plates which convert a corresponding plane polarized light beam incident thereon from the adjacent end of said source into a circularly polarized light beam and the oppositely advancing circularly polarized Light beam is converted back into a plane polarized light beam at a prescribed angle for propagation through the source. " _c .T.iGii4AL IMSPSCJED 009828/147 4 «23-16U607 4. Device according to claim 1, characterized in that that the polarization converters Faraday rotators are which the plane polarized light incident on it from the adjacent end of the source by 45 ° rotate so that the polarization of these rotated S1 numbers not through the optical cavity forming devices is disturbed, and also the oppositely progressing rays of light 45 ° in the opposite direction Direction to advance through the source can be rotated at a given orientation. 5 «Device according to claim 1, characterized in that: e k e η η ζ e i c h η et that continue polarizing devices between each end of the laser source and the polarization converters are provided to those of each end of the laser source to polarize mimicked, oppositely directed light beams at a given angle. 6. Device according to claim 1, characterized in that that the device for removing opposing light rays from the optical cavity - a partially permeable And is part of the optical cavity forming devices. 7. Device according to claim 6, characterized by polar arranged outside the ring-shaped ">? 00982S / 1 / .74 BAD OR5GSMAL 16U607 cation analyzing devices, devices for applying the first and second extracted light beams to the polarization analyzing device in collinear relation to direct and photodetector devices that are directed by the polarization analyzing directions address transmitted light. 8. Devices according to claim 7 »characterized in that the laser source is a gaseous laser medium containing tube (i4) which is closed at its ends by optical Brewster's angle surfaces (20, 21), which act as polarizing devices and wherein the optical cavity is designed in the manner of a polygon. 9 «Device according to claim 1, characterized in that that the device for removing the opposing light beams has a first partially transmitting part . for removing the first removed light beam, and that a second partially transmitting (permeable) Part is used to remove the second removed light beam, the first and second partially transmitting parts are part of the optical cavity forming devices. 10. Device according to claim 8, characterized by means of making the first and second extracted light beams collinear and a photodetector 00982 8/1 U 74 ^ _{M &} . BAD OFSGINAL 16H607 device that responds to these collinear beams of light. 11. Device according to claim 10, daduroh g e k e nn ζ e i c < h net that the laser source is one with a gaseous laser medium has a filled tube, which is closed at its ends by optical Brewster's angle surfaces, which act as a polarization device, and wherein the optical cavity is oriented polygonally. BAD ORiGüN 009828 / U74 Blank page